The invention relates to a process for the hydrogenation of unsaturated hydrocarbons, in which these unsaturated hydrocarbons are treated with anion exchangers prior to a catalytic hydrogenation which is in itself known.
When olefinic or diolefinic hydrocarbon fractions or hydrocarbon fractions containing acetylenes are hydrogenated, the deposition of impurities or the formation of polymers on the catalyst causes a progressive poisoning and deactivation of this catalyst, which results in a relatively short catalyst life. This applies particularly to the selective hydrogenation of diolefinic cracked gasoline fractions which are produced, for example, when ethylene is obtained by cracking naphtha, gas oils and the like.
Various processes are known for the selective hydrogenation of these cracked gasoline fractions and for their pretreatment before being employed in this partial hydrogenation (Asinger, Die Petrolchemische Industrie (The Petrochemical Industry), Akademie-Verlag Berlin, page 618 et seq.). These include pretreatments by heat, the removal of polymers by distillation, the removal of polymers from the hydrogenation catalyst by washing, employing trickle phases or liquid phase hydrogenation reactions in which partially hydrogenated hydrocarbon streams are recycled, and the general improvement of the hydrogenation catalyst. In these processes, catalyst lives of a few months up to a year, and only occasionally longer, are achieved. However, a relatively high outlay is required in the pretreatment for these processes, for example a high outlay of energy if polymers are removed by distillation and a high outlay of investment is hydrogenated product streams are recycled.
The hydrogenation of acetylene-containing or olefinic hydrocarbons also leads, as a result of the formation of polymers and as a result of the presence of impurities, to the catalyst surface becoming coated or the catalyst becoming poisoned and thus to an unsatisfactory catalyst life. Thus, for example, when dimers and oligomers from the oligomerization of C.sub.3 and C.sub.4 olefines are hydrogenated, catalyst lives of only a few months are achieved.
Our own attempts to employ intimate mixing of the hydrocarbon fractions to be hydrogenated with an aqueous solution having an alkaline reaction, as a pretreatment before the actual hydrogenation, have not led to any appreciable improvement in catalyst life.